Hayabusa Probably Didn’t Get a Sample After All

byFraser CainonDecember 9, 2005

Artist’s impression of Hayabusa spacecraft. Image credit: JAXA Click to enlarge
As has been reported, it is estimated that part of a series of attitude and orbit control commands to restore the Hayabusa from its safe-hold mode have not gone well, and the functions of its major systems, including its attitude and communication network, have significantly deteriorated. However, on Nov. 29, a beacon line through a low gain antenna was restored.

On Nov. 30, we started a restoration operation by turning on and off the radio frequency modulation through the autonomous diagnostic function. Subsequently, on Dec. 1, telemetry data were acquired at 8 bits per second through the low gain antenna, although the line was weak and often disconnected. According to the data transmitted so far, the attitude and orbit control commands sent on Nov. 27 did not work well due to an unknown reason, and either major attitude control trouble or a large electric power loss seems to have occurred. It is estimated that the overall power switching systems for many pieces of onboard equipment were reset as their temperature dropped substantially due to the evaporation of leaked propellant, and also because of a serious discharge of electricity from the batteries of many sets of onboard equipment and systems due to declining power generation. Details are still under analysis.

On Dec. 2, we tried to restart the chemical engine, but, even though a small thrust was confirmed, we were not able to restore full-scale operations. Consequently, the cause of the anomaly on Nov 27 is still under investigation, and we suspect that one of the causes could be the malfunction of the chemical engine.

On Dec. 3, we found that the angles between the axis of the onboard high gain antenna (+Z angle) and the Sun, and also that with the earth, had increased to 20 to 30 degrees. As an emergency attitude control method, we decided to adopt a method of jetting out xenon for the ion engine operation. Accordingly, we immediately started to create the necessary operation software. As we completed the software on Dec. 4, we changed the spin speed by xenon jet, and its function was confirmed. Without delay, we sent an attitude change command through this function.

As a result, on Dec. 5, the angle between the +Z axis and the sun, and the earth, recovered to 10 to 20 degrees, and the telemetry data reception and acquisition speed was restored to the maximum 256 bits per second through the mid gain antenna.

After that, we found that there was a high possibility that the projectile (bullet) for sampling had not been discharged on Nov. 26, as we finally acquired a record of the pyrotechnics control device for projectile discharging from which we were not able to confirm data showing a successful discharge. However, it may be because of the impact of the system power reset; therefore, we are now analyzing the details including the confirmation of the sequence before and after the landing on Nov. 26.

As of Dec. 6, the distance between the Hayabusa and the Itokawa is about 550 kilometers, and that from the earth is about 290 million kilometers. The explorer is relatively moving from the Itokawa toward the earth at about 5 kilometers per hour.

We are now engaging in turning on, testing, and verifying onboard equipment of the Hayabusa one by one to start the ion engine. We currently plan to shift the attitude control to one using the Z-axis reaction wheel, and restart the ion engine. The restart is expected to happen no earlier than the 14th. We are currently rescheduling the plan for the return trip to earth. We need to study how to relax the engine operation efficiency. We will do our utmost to solve the problem with the attitude control (such as the restoration of the chemical engine), then find a solution for the return trip.